package main

import (
	"fmt"
	"image"
	"image/color"
	"image/png"
	"math"
	"os"

	"github.com/EliCDavis/vector"
	"github.com/EliCDavis/vector/vector2"
	"github.com/EliCDavis/vector/vector3"
)

type Field[T vector.Number] func(v vector3.Vector[T]) float64

func Sphere[T vector.Number](pos vector3.Vector[T], radius float64) Field[T] {
	return func(v vector3.Vector[T]) float64 {
		return v.Distance(pos) - radius
	}
}

func Box[T vector.Number](pos vector3.Vector[T], bounds vector3.Vector[T]) Field[T] {
	halfBounds := bounds.Scale(0.5)
	// It's best to watch the video to understand
	// https://www.youtube.com/watch?v=62-pRVZuS5c
	return func(v vector3.Vector[T]) float64 {
		q := v.Sub(pos).Abs().Sub(halfBounds)
		inside := math.Min(float64(q.MaxComponent()), 0)
		return vector3.Max(q, vector3.Zero[T]()).Length() + inside
	}
}

func Union[T vector.Number](fields ...Field[T]) Field[T] {
	return func(v vector3.Vector[T]) float64 {
		min := math.MaxFloat64

		for _, f := range fields {
			fv := f(v)
			if fv < min {
				min = fv
			}
		}

		return min
	}
}

func Intersect[T vector.Number](fields ...Field[T]) Field[T] {
	return func(v vector3.Vector[T]) float64 {
		max := -math.MaxFloat64

		for _, f := range fields {
			fv := f(v)
			if fv > max {
				max = fv
			}
		}

		return max
	}
}

func Subtract[T vector.Number](minuend, subtrahend Field[T]) Field[T] {
	return func(f vector3.Vector[T]) float64 {
		return math.Max(minuend(f), -subtrahend(f))
	}
}

func Translate[T vector.Number](field Field[T], translation vector3.Vector[T]) Field[T] {
	return func(v vector3.Vector[T]) float64 {
		return field(v.Sub(translation))
	}
}

func evaluateAtDepth[T vector.Number](dimension int, field Field[T], depth T, i int) {
	img := image.NewRGBA(image.Rectangle{
		image.Point{0, 0},
		image.Point{dimension, dimension},
	})

	for x := 0; x < dimension; x++ {
		for y := 0; y < dimension; y++ {
			v := field(vector3.New[T](T(x), T(y), depth))
			byteVal := (v / float64(dimension/20)) * 255
			var c color.Color
			if v > 0 {
				c = color.RGBA{R: 0, G: 0, B: byte(byteVal), A: 255}
			} else {
				c = color.RGBA{R: 0, G: byte(-byteVal), B: 0, A: 255}
			}
			img.Set(x, y, c)
		}
	}

	f, err := os.Create(fmt.Sprintf("field_%04d.png", i))
	if err != nil {
		panic(err)
	}
	defer f.Close()

	err = png.Encode(f, img)
	if err != nil {
		panic(err)
	}
}

func main() {
	dimension := 512
	quarterDim := float64(dimension) / 4.

	middleCoord := vector2.
		Fill(dimension).
		Scale(0.5).
		ToFloat64()

	middleCord3D := vector3.New(middleCoord.X(), middleCoord.Y(), 0)

	smallRing := Subtract(
		Sphere(middleCord3D, 100),
		Sphere(middleCord3D, 50),
	)

	field := Intersect(
		Subtract(
			Sphere(middleCord3D, 200),
			Sphere(middleCord3D, 100),
		),
		Union(
			Translate(smallRing, vector3.New(1., 1., 0.).Scale(quarterDim)),
			Translate(smallRing, vector3.New(1., -1., 0.).Scale(quarterDim)),
			Translate(smallRing, vector3.New(-1., 1., 0.).Scale(quarterDim)),
			Translate(smallRing, vector3.New(-1., -1., 0.).Scale(quarterDim)),
			Box(middleCord3D, middleCord3D),
		),
	)

	for i := 0; i < 100; i++ {
		evaluateAtDepth(dimension, field, float64(-dimension/2)+(float64(i*dimension)*0.01), i)
	}
}